This invention relates to apparatus for pulling tubes from tube sheets.
Many heat exchangers comprise a pair of parallel tube sheets, a plurality of baffle plates, and a multitude of heat exchange tubes. The tube sheets are located at the ends of the heat exchanger; the baffle plates are positioned between the tube sheets, generally parallel thereto; and the heat exchange tubes extend between the tube sheets, through the baffle plates, and are supported by the tube sheets. The tube sheets and baffle plates have a series of aligned holes formed therein, and the heat exchange tubes are inserted through these holes and then expanded in the areas of the tube sheets into pressure contact therewith. This pressure contact securely holds the tubes in position and forms a fluid tight seal between the tube sheets and the tubes. In operation, a first heat transfer fluid such as water is conducted through the tubes between the tube sheets, and a second heat transfer fluid having a temperature different than that of the first heat transfer fluid is conducted past the exterior of the tubes between the tube sheets, indirectly transferring heat between the two heat transfer fluids.
At times, due to malfunctions or normal maintenance, it is necessary to remove one or even all of the tubes used in a heat exchanger of the general type described above. Commonly this is done by first relieving the pressure forces between the tubes and the tube sheets and then longitudinally pulling the tubes through the baffle plates and the tube sheets. Manually pulling the tubes through the baffle plates and the tube sheets is often a difficult, time consuming task since the tubes in some heat exchangers may have length of up to 70 feet and be of considerable weight. Consequently, attention has been directed to designing machines for pulling the tubes from heat exchangers of the type discussed above.
Ideally, a mechanical tube pulling apparatus should meet or satisfy a number of goals. For example, it is desirable that the apparatus be able to twist or to rotate a tube about its longitudinal axis as the tube is pulled through a heat exchanger. More specifically, during normal operation of the heat exchanger, corrosion and other particulates or debris accumulate on the exterior surfaces of the heat transfer tubes. As a tube is pulled through the baffle plates and the tube sheets of the heat exchanger, these particulates may jam between the tube and the baffle plates or tube sheets, retarding or possibly stopping movement of the tube. Usually, by slightly rotating or twisting the tube about its longitudinal axis as the tube is pulled through the baffle plates and the tube sheets, these particulates or debris may be broken off from the tube surface, effectively preventing the particulates from jamming tube movements.
In addition, it is preferable that the tube pulling apparatus be employable with tubes of various diameters and of various styles, and that the apparatus be able to develop different tube gripping pressures, resulting in a very flexible and highly adaptable apparatus. Further, it is desirable to maximize the number of steps or operations performed by the tube pulling apparatus itself, minimizing the amount of human labor needed to pull the tubes from the heat exchanger. Finally, of course, it is desirable to keep the design, construction, and operation of the tube pulling apparatus relatively simple and to minimize the number of parts or elements of the apparatus to insure reliability as well as to minimize manufacturing, operating, and maintenance costs.